light hurts fish

Question
Thank you for your help, but my fish aren't tropical, they are freshwater. And I just did clean out the tank a few days ago and let it sit with the filter running to declorinate it.  I'm afraid to use water conditioner because last time I did all the fish died.  Any ideas?
Thanks,
Bill

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Followup To
Question -
Hello. After all my fish died last time I took a long time before getting more. I belive the problem was that I misjudged the size of the tank and over medicated them. I haven't put anything in the water except some liquid microbacteria, and just a bit of that. I didn't put anything in the water to declorinate it, I just let it sit for 5 days with the filter running. The water in Taiwan is very bad.
Now the problem. Yesterday when I got the fish they were all fine. I got two bottom feeders (yellow with black tiger-stripes) and some food for them. Today, I found one laying on the bottom of the tank and the other hiding under something. I turned off the light to see what would happen. The hider came out and started scutting around. The other perked up but didn't mover around much. When I turned the light on again, the hider hid again and the other flopped on his side. I've got the light off now, but the little fish (guppies?) are laying on the bottom when it's dark.
I've had trouble with fish and light before. I was keeping two newts in this tank with a small light just on one side. After a few days, the gravel and the decorations (little fence) had turned a burnt orange color. It cleaned off easily. I'm worried that there is something in the water that is reacting with the light. Or could it be the microbacteria that I added in?
Also, the one sick (non-hiding) bottom feeder's head looks black unlike the hider.
I don't know about the ph, nitrate, or ammonia values or how to go about measuring them.
Hope you can help, it would be quite depressing to loose any more of these guys. Thanks,
Bill
Answer -
hello i could only recomend that you take all the fish out of the tank and set them in individual containers (temporaily) and tottaly clean out the tank...like a major clean out!!! then set your filter in then add all your objects and rocks in the tank. (make sure to soak all plants and rocks in a water conditioner for atleast an hour! then add water into the tank at about 72F and then put in some water conditioner into the tank (you can get it at local pet stores) mix it all around and then wait half an hour with pump on! then slowly add fish, smallest to biggest. (tropical fish love light so what i think is that you have to do is get another tank and put bottem hinding fish into another tank) let them be and hopfully this will clear your problem! hope this helps...

  P.S tell me how that works for you later on ;)

  thanks...*maggana*

Answer
hello again...sorry but since i havent seen the tank i do not know what it lookes like and what conditioner you used...the only thing i could suggest is that to leave the tank running for more than 24 hours at least?...or your fish dont work together? hope this helps? bubi feel free to ask any more questions
  *maggana*